Ethernet via Thunderbolt display with MacBook Pro 2017 (A1707)?
Solution 1:
It looks like this other post provided the hint that I needed to get this working! MacBook Sierra display ethernet needs constant re-starting
Unplugging the display and then plugging it back in fixed the problem! What a pain!
Solution 2:
According to this the trick is:
To get the ethernet on the display working, I had to disconnect the USB-C adapter, delete (AFAIR) the Thunderbolt Bridge from the network preferences, and then reconnect the adapter.
This worked for me too, I now have Display Ethernet in the network interfaces list.